Drilling Adjacent to Salt Bodies: Definition of Mud Weight Window and Pore Pressure Using Numerical Models and Fast Well Planning

Abstract

Abstract A 3D finite-element model covering more than 10 blocks in the deepwater Green Canyon area of the Gulf of Mexico has been used to calculate the stress distribution around an extensive salt body. The complex model geometry, and the determination of rock properties and pore pressure, was based on multiclient seismic data and state-of-the-art imaging techniques. The model has been used to determine the impact that salt geometry will have on drilling decisions. The numerical model shows that the near-salt stresses are dependent mainly on the morphology of the salt body. Higher compressive stresses were found in supra-salt minibasins and sub-salt concave-down embayments, resulting in higher mud weight windows. Areas below convex-down allochthonous base salt show lower compressive stresses, resulting in narrow mud weight windows. A fast well planning tool has been developed to translate the results of the finite-element model to operational parameters for well design. With this tool, the full stress tensors are extracted along any arbitrary well trajectory, providing a high-resolution model for calculating the mud weight window. This allows the drilling engineer to create fast predictions along any chosen trajectory within the study area and to make quick comparisons of the drilling mud weight window along multiple trajectories, helping with the selection of the optimal wellpath design. The application of this tool is illustrated using a "case study" focused on four proposed trajectories for a hypothetical well that has to reach the Eocene-Paleocene Wilcox formation.